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digitalmars.D - From APL

reply "bearophile" <bearophileHUGS lycos.com> writes:
The paper touches only a small subset of what's needed to write 
modern program, it's mostly about array operations and related 
matters. It compares some parts of the old Fortran 88 with parts 
of the dead APL language. The author seems fond of APL, and 
several things written in the paper are unfair:

"Fortran 88 Arrays - Paper Clips and Rubber Bands" (2001), by 
Robert Bernecky:
http://www.snakeisland.com/fortran8.htm

Some of the ideas of APL are widely used in modern functional 
languages. D contains array operations and Phobos contains some 
higher order operations similar to some APL verbs and adverbs.

------------------

Section 2.3 is about Scan operations, that are like reduce or 
fold, but keep all the intermediate results too:

+\ of 3 1 2 4

is 3 4 6 10

Some lazy scans are present in the Haskell Prelude too (and in 
Mathematica) (the Prelude contains functions and constants that 
are loaded on default):
http://zvon.org/other/haskell/Outputprelude/scanl_f.html

I think scans are not present in Phobos. Maybe one or two are 
worth adding.

------------------

Section 2.5 suggests to generalize the dot product:

If the + and * of the Fortran 77 DO loops for inner product are 
replaced by other functions, a whole family of interesting inner 
products appear,<

Some examples of usage (in J language): Associative search *./..=y Inverted associative x+./..~:y Minima of residues for primes x<./..|y Transitive closure step on Booleans y+./..*.y Minima of maxima x<./..>.y Maybe a higher order function named "dot" (that takes two callables) is worth adding to Phobos. But I am not sure. ------------------ Section 2.6 reminds us that a transpose() is a commonly useful function. A transpose is handy to have in Phobos. Bye, bearophile
Sep 20 2012
parent "Simen Kjaeraas" <simen.kjaras gmail.com> writes:
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On Thu, 20 Sep 2012 13:55:48 +0200, bearophile <bearophileHUGS lycos.com>  
wrote:

 Section 2.3 is about Scan operations, that are like reduce or fold, but  
 keep all the intermediate results too:

 +\ of 3 1 2 4

 is 3 4 6 10

 Some lazy scans are present in the Haskell Prelude too (and in  
 Mathematica) (the Prelude contains functions and constants that are  
 loaded on default):
 http://zvon.org/other/haskell/Outputprelude/scanl_f.html

 I think scans are not present in Phobos. Maybe one or two are worth  
 adding.

See attached. Mayhaps I should post this as a pull request?
 ------------------

 Section 2.5 suggests to generalize the dot product:

 If the + and * of the Fortran 77 DO loops for inner product are  
 replaced by other functions, a whole family of interesting inner  
 products appear,<

Some examples of usage (in J language): Associative search *./..=y Inverted associative x+./..~:y Minima of residues for primes x<./..|y Transitive closure step on Booleans y+./..*.y Minima of maxima x<./..>.y Maybe a higher order function named "dot" (that takes two callables) is worth adding to Phobos. But I am not sure.

So that's basically mapReduce, right? We've got that, just not as succinct. -- Simen ------------QLwcgRpqxl91mosI3qOrko Content-Disposition: attachment; filename=scan.d Content-Type: application/octet-stream; name="scan.d" Content-Transfer-Encoding: Base64 aW1wb3J0IHN0ZC5hbGdvcml0aG07CmltcG9ydCBzdGQucmFuZ2U7CmltcG9ydCBz dGQudHJhaXRzOwppbXBvcnQgc3RkLmZ1bmN0aW9uYWw7CmltcG9ydCBzdGQudHlw ZXR1cGxlOwoKdGVtcGxhdGUgc2NhbihhbGlhcyBmdW4pCnsKICAgIGF1dG8gc2Nh bihULCBSYW5nZSkoVCBzdGFydCwgUmFuZ2UgcikgaWYgKGlzSW5wdXRSYW5nZSEo VW5xdWFsIVJhbmdlKSkKICAgIHsKICAgICAgICBhbGlhcyBiaW5hcnlGdW4hZnVu IF9mdW47CiAgICAgICAgCiAgICAgICAgc3RydWN0IFJlc3VsdAogICAgICAgIHsK ICAgICAgICAgICAgYWxpYXMgVW5xdWFsIVJhbmdlIFI7CiAgICAgICAgICAgIGFs aWFzIHR5cGVvZihfZnVuKFQuaW5pdCwgLkVsZW1lbnRUeXBlIVIuaW5pdCkpIEVs ZW1lbnRUeXBlOwogICAgICAgICAgICBSIF9pbnB1dDsKICAgICAgICAgICAgRWxl bWVudFR5cGUgX2Zyb250OwogICAgICAgICAgICAKICAgICAgICAgICAgdGhpcyhU IHN0YXJ0LCBSIGlucHV0KQogICAgICAgICAgICB7CiAgICAgICAgICAgICAgICBf ZnJvbnQgPSBzdGFydDsKICAgICAgICAgICAgICAgIF9pbnB1dCA9IGlucHV0Owog ICAgICAgICAgICB9CgogICAgICAgICAgICBzdGF0aWMgaWYgKGlzSW5maW5pdGUh UikKICAgICAgICAgICAgewogICAgICAgICAgICAgICAgLy8gUHJvcGFnYXRlIGlu ZmluaXRlLW5lc3MuCiAgICAgICAgICAgICAgICBlbnVtIGJvb2wgZW1wdHkgPSBm YWxzZTsKICAgICAgICAgICAgfQogICAgICAgICAgICBlbHNlCiAgICAgICAgICAg IHsKICAgICAgICAgICAgICAgIGJvb2wgX2VtcHR5ID0gZmFsc2U7CiAgICAgICAg ICAgICAgICBAcHJvcGVydHkgYm9vbCBlbXB0eSgpCiAgICAgICAgICAgICAgICB7 CiAgICAgICAgICAgICAgICAgICAgcmV0dXJuIF9lbXB0eTsKICAgICAgICAgICAg ICAgIH0KICAgICAgICAgICAgfQoKICAgICAgICAgICAgdm9pZCBwb3BGcm9udCgp CiAgICAgICAgICAgIHsKICAgICAgICAgICAgICAgIHN0YXRpYyBpZiAoIWlzSW5m aW5pdGUhUikgewogICAgICAgICAgICAgICAgICAgIGlmIChfaW5wdXQuZW1wdHkp IHsKICAgICAgICAgICAgICAgICAgICAgICAgX2VtcHR5ID0gdHJ1ZTsKICAgICAg ICAgICAgICAgICAgICB9CiAgICAgICAgICAgICAgICB9CiAgICAgICAgICAgICAg ICBpZiAoIWVtcHR5KSB7CiAgICAgICAgICAgICAgICAgICAgX2Zyb250ID0gX2Z1 bihfZnJvbnQsIF9pbnB1dC5mcm9udCk7CiAgICAgICAgICAgICAgICAgICAgX2lu cHV0LnBvcEZyb250KCk7CiAgICAgICAgICAgICAgICB9CiAgICAgICAgICAgIH0K ICAgICAgICAgICAgCiAgICAgICAgICAgIEBwcm9wZXJ0eSBhdXRvIHJlZiBmcm9u dCgpCiAgICAgICAgICAgIHsKICAgICAgICAgICAgICAgIHJldHVybiBfZnJvbnQ7 CiAgICAgICAgICAgIH0KICAgICAgICAgICAgCiAgICAgICAgICAgIHN0YXRpYyBp ZiAoaGFzTGVuZ3RoIVIgfHwgaXNTb21lU3RyaW5nIVIpCiAgICAgICAgICAgIHsK ICAgICAgICAgICAgICAgIEBwcm9wZXJ0eSBhdXRvIGxlbmd0aCgpCiAgICAgICAg ICAgICAgICB7CiAgICAgICAgICAgICAgICAgICAgcmV0dXJuIF9pbnB1dC5sZW5n dGg7CiAgICAgICAgICAgICAgICB9CgogICAgICAgICAgICAgICAgYWxpYXMgbGVu Z3RoIG9wRG9sbGFyOwogICAgICAgICAgICB9CgogICAgICAgICAgICBzdGF0aWMg aWYgKGlzRm9yd2FyZFJhbmdlIVIpCiAgICAgICAgICAgICAgICBAcHJvcGVydHkg YXV0byBzYXZlKCkKICAgICAgICAgICAgICAgIHsKICAgICAgICAgICAgICAgICAg ICBhdXRvIHJlc3VsdCA9IHRoaXM7CiAgICAgICAgICAgICAgICAgICAgcmVzdWx0 Ll9pbnB1dCA9IHJlc3VsdC5faW5wdXQuc2F2ZTsKICAgICAgICAgICAgICAgICAg ICByZXR1cm4gcmVzdWx0OwogICAgICAgICAgICAgICAgfQogICAgICAgIH0KCiAg ICAgICAgcmV0dXJuIFJlc3VsdChzdGFydCwgcik7CiAgICB9Cn0KCnVuaXR0ZXN0 IHsKICAgIGF1dG8gYXJyID0gc2NhbiEoKGEsYik9PmErYikoMCwgWzEsMiwzLDRd KTsKICAgIAogICAgYXNzZXJ0KGVxdWFsKGFyciwgWzAsMSwzLDYsMTBdKSk7CiAg ICAKICAgIGltcG9ydCBzdGQuc3RkaW87CiAgICAKICAgIHdyaXRlbG4oIHNjYW4h ImErYiIoMCwgY2FzdChpbnRbXSlbXSkgKTsKfQoKdm9pZCBtYWluKCApIHsKCn0= ------------QLwcgRpqxl91mosI3qOrko--
Sep 21 2012